1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses that form an image by primary-transferring a toner image, which is a developer image formed on a drum-type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum), to an intermediate transfer member and by further secondary-transferring the primary-transferred toner image to a recording material (recording medium) are in practical use.
In obtaining a good image from an image forming apparatus which uses an intermediate transfer member, it is important to remove secondary transfer residual toner (residual toner), which remains on the intermediate transfer member and is untransferred from the intermediate transfer member to the recording material at the secondary transfer, from the intermediate transfer member before the next primary transfer is started.
Conventionally, the secondary transfer residual toner of the previous printing is removed by a cleaning method, which uses rubbing, before the primary transfer. According to the rubbing method, the toner is removed by a fur brush or a blade. The fur brush or the blade is provided at a position downstream of a secondary transfer unit of the intermediate transfer member and upstream of a primary transfer unit, in the moving direction of the intermediate transfer member.
If the cleaning method using the rubbing method is used, since the surface of the intermediate transfer member is scraped, the surface of the intermediate transfer member may be deteriorated or the toner may be easily fused and adhered to the intermediate transfer member. Further, since a dedicated container for collecting the removed secondary transfer residual toner is necessary, the image forming apparatus needs to have an extra space for the container. Thus, in recent years, a charging cleaning method discussed in Japanese Patent Application Laid-Open No. 9-50167 has been used to solve such a problem. According to the charging cleaning method, secondary transfer residual toner on an intermediate transfer member is collected in a cleaning device of a photosensitive drum.
Further, according to the charging cleaning method, the secondary transfer residual toner on the intermediate transfer member is charged opposite in polarity to the charging potential of the photosensitive drum by a charging unit provided downstream of a secondary transfer position in the rotational direction of intermediate transfer member and upstream of a primary transfer position. Thus, the secondary transfer residual toner is transferred to the photosensitive drum at the primary transfer portion.
The toner transferred to the photosensitive drum is collected by the cleaning device of the photosensitive drum. A common cleaning device of the photosensitive drum includes a cleaning blade (cleaning unit) which contacts the photosensitive drum and a waste toner container where the toner scraped from the photosensitive drum by the cleaning blade is collected.
According to the charging cleaning method, since the charging unit does not need to strongly contact and scrape the intermediate transfer member, deterioration of the surface of the intermediate transfer member and toner fusion to the intermediate transfer member can be prevented compared to the cleaning method employing the rubbing. Further, since the residual toner collected after the cleaning operation is collected in a waste toner container of the cartridge, it is not necessary to prepare a container dedicated for storing the collected residual toner. This contributes to reducing the size and cost of the image forming apparatus.
However, according to the charging cleaning method, if the cleaning blade of the photosensitive drum is to clean a large amount of toner to be received especially when the image forming apparatus is recovered from a paper jam during high quality printing in a low temperature environment, a defective image may be formed due to poor cleaning. According to the charging cleaning method, since the residual toner is charged to a polarity opposite to the polarity of the photosensitive drum, the residual toner tends to strongly adhere to the photosensitive drum due to static electric charge. If the cleaning blade is to scrape a large amount of such toner, the cleaning blade may be deformed and the toner may slip through the cleaning blade.